Wick U.S. Pat. No. 2,733,199 discloses a process for cathodically depositing chromium films on metal from a solution while Wesley et al U.S. Pat. No. 2,844,530 describes the electrodeposition of a black nickel coating on metal.
U.S. Pat. No. 2,917,817 to Tabor is directed to thin exposed light absorptive and heat transparent surface coatings, which are in heat conductive relation to a bright metal base. Solar heating panels utilizing these coatings have been expensive and difficult to produce.
McDonald U.S. Pat. No. 4,055,707 describes a black chrome coating for solar panels which is electroplated onto a metal substrate. Several electroplating solutions are described in this patent.
Scholz et al U.S. Pat. No. 4,080,269 discloses a method for producing a black coating which is highly absorbant in the solar spectrum range using electrodeposition from an aqueous solution containing a soluble cobalt compound. A large amount of alkali thiocyanate is used in the disclosed process.
A process for depositing an oxide layer from a solution containing a metal salt and isopropynol is disclosed in Mackey U.S. Pat. No. 4,094,705. The patent fails to mention the solar absorption properties of the oxide layer.
Schardein et al U.S. Pat. No. 4,104,136 describes a process for applying thin metal coatings to a substrate for solar energy absorption. The process provides for electrochemically plating a clean aluminum surface in a solution containing ammonium molybdate.